1. Field
The following description relates to an interferometer for measuring a TSV and a measurement method using the same, for example, to an interferometer that comprises a variable field stop and thus is capable of measuring a diameter and length of a via hole having a large aspect ratio such as a TSV (Through Silicon Via) formed on a silicon semiconductor, and a measurement method using the same.
2. Description of Related Art
Recently, in the semiconductor field as well, 3-dimensional chips are emerging as alternatives to overcome the limitations of 2-dimensional refining technologies having limited chip size area.
The concept of a 3-dimensional structure has already been in use in the packaging industry. However, according to existing methods, various terminals are disposed in only one surface of a semiconductor chip, and it is necessary to electrically connect signal terminals of a plurality of chips using wire bonding. Therefore, there are problems in terms of size of the chips, complexity of wiring, and electricity consumption etc.
Therefore, in order to overcome these problems, TSV (Through Silicon Via) technology was proposed where an electrode is formed such that it penetrates a silicone that is the material of semiconductor substrate, thereby providing a signal transduction pathway just as an elevator in a high rise building.
Such a TSV technology is expected to be effective in terms of the degree of circuit agglomeration, operating speed, power consumption, and manufacturing cost etc., and thus researches are being concentrated in the TSV technology.
Conventional interferometers are used as TSV measurement apparatuses for forming and inspecting the state of formation of the TSVs.
The most representative interferometer is White Light Interferometer (WLI) that splits the light coming out from one light source into two lights, makes the two lights proceed at a perpendicular angle from each other and then makes them meet each other, and then forms interference fringes by the optical path difference of the two lights.
Using the above principle, it is possible to measure the characteristics of the surface topology of a thin film such as a silicone semiconductor wafer.
FIG. 1 is a schematic view of a white light interferometer. With reference to FIG. 1, a white light interferometer splits the light generated from light source 110 in two directions that are perpendicular to each other through a beam split 120, reflects one of the split light through a mirror 130, while reflecting the other split light through a measurement object 140, and then makes the two reflected lights to be re-injected into the beam split.
Next, the lights re-infected into the beam split 120 are combined with each other as they pass the beam split 120, and interference fringes are formed on a CCD 150 through an object lens 170 and relay lens (not illustrated).
Herein, by the piezoelectric sensor 180, the object lens 170 is moved in an optical path direction, thereby adjusting the optimal focal length of the object lens 170.
Herein, since white light has a short interference distance, when measuring a certain amount of white light regarding a measurement object, interference phenomenon occurs starting from the highest place of the measurement object. That is, the interference fringes occur only at the optimal focal length of the object lens 170.
Therefore, it is possible to identify which part is high and which part is low by checking the changes in the light intensity of an unknown measurement object. Herein, the height of the measurement object may be obtained by an analyzing means.
That is, based on the interference fringes, one can know which part is high and which part is low. Herein, the heights can be measured through the piezoelectric sensor 180.
In the aforementioned interferometer, it is possible to use the piezoelectric sensor 180 to move the object lens 170 in the direction of the measurement object so that an image is formed on the CCD at every certain interval.
Using the interferometer, when measuring the surface of a thin film such as a wafer, it is possible to analyze the height of the measurement object after moving the piezoelectric sensor 180 once.
However, in the case of a conventional interferometer, when a wide-angle lens is used to inject light to TSV, the incidence angle of the light injected into the TSV is bigger than the diameter of the via hole, and thus only a small amount of light is actually injected inside the TSV. Consequently, the light may not reach the bottom surface.
Furthermore, even when the light source was replaced so as to increase the intensity of the light reaching the bottom surface, since the focus of light has to be measured at every certain distance in the direction of the TSV, it takes a long time to measure the focus of the light, increasing the capacity of the result data, thereby overloading the entire system.